Dielectric heating and pressing die structure



Jan. 5, 1960 R. M. sTALLARD 2,920,172

DIELECTRIC HEATING AND PRESSING DIE STRUCTURE Filedct, 4. 195e INVENn'm ATVQQNEY IHELECTRIC` HEATING AND PRESSING DIE STRUCTURE Ralph M. Stallard, Utica, Mich., assignor to General Motors Corporation, Detroit, Mich., a corporation of Delaware Application ctober-4, 1956, Serial No. 613,906

Claims. (Cl. 219-10.53)

This invention relates to novel die structure for dielectric heating and pressing apparatus.

In press apparatus employing the dielectric heating principle for working material, electrical arcing is a problem since it damages the electrodes as well as the material. For example, when embossing fabric pads, a concentrated electric-field develops near the edges of the pad. Since the surrounding air is a weak dielectric and easily ruptured by this concentration, arcing occurs between adjacent electrodes in the proximity of the pad edges or with a metalized fabric pad between one of the electrodes and the edges. These edges are burned and scorched bysparks from the arcing and must be cut away, both an extra time consuming operation and a waste of material. When the arcing is between the electrodes, they become pitted.

With these and other considerations in mind the present invention contemplates as a primary'object the provision of novel die structure especially adapted to eliminate undesired electrical arcing.

Specifically, the invention seeks to provide die structure including a pair' of die elements with one a spacer die element for positioning the work material a predetermined distance from the origin of the electrical arc and for' enabling the electrodes to be spaced further apart, thus eliminating the arc possibility. In addition, the configuration and disposition of the related die elements is such that the direction of the electric fields is controlled to prevent arcing.

Further, the invention provides, for some applications, resilient means for distributing and equalizing pressures which otherwise tend to injure the workpiece.

The foregoing and other object sand advantages of the invention will be apparent from the following description and from the accompanying drawings, in which:

Figure 1 is a'schematic view of an apparatus embodying the principles of this invention.

Figure 2 is a schematic view of a modified apparatus incorporating the invention.

Figure 3 isr a perspective view of work material formed in the Figure l apparatus.

Figure 4 is a perspective view of work material formed in the Figure 2 apparatus.

Briefly, the dielectric method of heating material is based on the condenser or capacitor principle. The material to be heated is placed between a pair of electrode or capacitor members which are subjected to a high frequency voltage lfrom a suitable source. Initially, when these members are charged, a polarity is established with the negatively charged particles being repelled by the negative member and attracted by the positive member. Then, the polarity is reversed as is the electronic action. vBy rapidly alternating the potential difference on the members, the Vcharged Aparticle movement back and forth generates heat in the dielectric between the electrode members.

In Figure 1, an arrangement is demonstrated especially adapted Vfor embossing some heat and pressure 2 sensitive fabric material, suchas a fabric pad 10 illustrated in Figure 3. A press element or 4embossing die 12 having embossing ribs, (not shown) to provide the Figure 3 pattern is supported by an upper press platen 14. Below this upper press platen 14 is a lower press platen 16 properly insulated and having mounted thereon a capacitor or electrode member 18 of good conducting material, such as aluminum. Disposed in consecutive` order from and supported by this electrode member 18 is a resilient member 20 ofn material with excellent dielectric insulating properties, such as butyl rubber, a spacer element or imager die 22 of electrically conductive material, another resilient sheet member 24 of heat resistant resilient material, eg., silicone rubber, and the fabric pad 10. Between thee'lectrodje member 18 uand the embossing die 12, which die yfunctions as an electrode, a means, e.g., `some vtype of high frequency generator designated generally at 26, is provided for applying a high frequency voltage 'betweenv the electrodes. The` press is operated in,a known manner simultaneously subjecting the pad 1l)y to a prescribedl pressure and a dielectric heat which togetherresult in the desired embossed pattern beingimpressedin the pad.

It will be noted that the embossing die k12 is larger than the fabric pad 10 and the fabric pad 10 is larger than the image die 22.` Since the image die 22, in effect, becomes an electrode (energy is transferred through the butyl rubber by means of a high frequency capacity coupling), the electric field will be drawn `inwardly along ay path4 ,thatwill noticause destructive arcing, e.g., along the broken vlines 2 8, from the embossing die 12 to the image die 22`-when the fabric pad 10, which constitutes a relatively strong dielectric compared to air, is` heated. Also, the edges of the dies 12 and 22 are preferably rounded to prevent point concentration of the field. Without the image die.22, the electric field would extend from the edges of the embossing die 12 through the air, a weak dielectric, tothe lower press platen 1.6 and electrode member 18` causing electrical arcing with the resultant sparks burning the edges of the pad 10. The thickness of the image die 22 maybe varied, as desired, to insure that the distance. between the embossing die and ythe-lower press platen l'jand electrode mem-ber 18 is suiiiciem to discourage any `arcing tendency.

The resilient members 20 and y24 are employed principally to equalize and distribute pressures during the pressing operation, thus insuring even embossing patterns Without damaging the fabric, avaluable feature with delicate fabrics. In addition, the heat resistant resilient material provides additional protection against electrical arcing. Of course, one or both of these members 20 and 24 may be eliminated in certain applications.

The arrangement'in Figure 2 is very similar to that in Figure 1 with the principles of operation being the same. An embossing die 12f.is secured to the upper press platen 14 as Vinthe Figure 1 embodiment, and an electrically conductive imagey die 22 is supported by the electrode member'18.V Between the dies 12' and 22' Va fabric pad 30 of heat and pressure sensitive material, such as that in Figure 4, is inserted having a metalized facing or surface 32. The pad 30 is shown extending consider-ably beyond the dies 12 and 22 for illustration, however the pad may be overlapped by the embossing die 12.r as in Figure 1. When the press is closed, the pad 3.0 is subjected to the high frequency voltage from the generator .2,6 giving the embossed pattern effect depicted in Figure 4.

In this Figure 2 arrangement the metalized surface 32, in effect, becomes a .part of the embossing die 12' with Vapproximately the same voltage. the absence of ythe image die 22 arcing would occur at the edges of the pad 30 along the lines 34. But with As aa result, in

the image die 22' disposed as shown, the edges are moved from the electrode member 18 a sufficient distance that arcing will not occur with the voltages being used. As in Figure l, the corners of the dies 12' and 22 are rounded and the image die 22 is smaller than the embossing die 12 to direct the electric eld inwardly along the lines 36 away from the electrode member 18.

My eliminating this undesired arcing, pads of material may be cut to the intended size and embossed without any necessity of later trimming away burned and scorched edges. Another important consideration and advantage is that with the Figure land 2 arrangements, a greater voltage may be employed without concern for arcing, hence speeding up the embossing operation and saving time.

It should be understood that the relative sizes of the various parts may be varied to achieve the best results as determined by the application and that the sizes shown herein are only for demonstration purposes.

I claim:

l. Apparatus for dielectrically heating and working heat yand pressure sensitive material comprising, in combination, an electrically conductive spacer element and a. press element disposed on opposite sides of the material in pressing relation therewith, an electrode member associated with said spacer member, means for applying high frequency voltage between said electrode member and said press element to dielectrically heat the material, said spacer member spacing the material a predetermined distance from the electrode to prevent electrical arcing between the press element and .the electrode member at the edges of the material.

2. Apparatus for dielectrically heating and working heat and pressure sensitive material comprising, in combination, an electrically conductive spacer element and a' press element disposed on opposite sides of the material in pressing relation therewith, an electrode member associated with said spacer element opposite the material, means vfor applying high frequency voltage between said press element and said electrode member to dielectrically heat the material, said press element extending beyond and overlapping said spacer element so as to cause an electric field to be directed inwardly towards said spacer element thereby preventing destructive arcing at the edges of the material.

3. Apparatus for dielectrically heating and working heat and pressure sensitive material comprising, in cornbination, yan electrically conductive spacer element and a. press element disposed on opposite sides of the material in pressing relation therewith, an electrode member associated with said spacer member opposite the material, means for applying high frequency voltage between said press element and said electrode member to dielectrically heat the material, said spacer member spacing the material a predetermined distance from said electrode member, said press element extending beyond and overlapping said spacer element so as to cause an electric field to be directed inwardly towards said spacer element, the spacing and directing by said spacer element preventing destructive arcing at the edges of the material. a

4. Apparatus for dielectrically heating and working heat and pressure sensitive material comprising, in combination, an electrically conductive spacer element and a press element having rounded edges and disposed on opposite sides of the material in pressing relation therewith, an electrode member associated with a part of said spacer element opposite the material, means for applying high frequency voltage between said press element and s aid electrode member to dielectrically heat the material, said spacer member spacing the Vmaterial a predetermined distance from said electrode member, said press element extending beyond and overlapping said spacer element so as to cause an electric field to be directed inwardly towards said spacer element, the spacing and directing by said spacer element preventing destructive arcing at the edges of the material.

5. Apparatus for dielectrically heating and working heat and pressure sensitive material comprising, in combination, an electrically conductive spacer element and a press element disposed on opposite sides of the material in pressing relation therewith, said spacer and press elements having rounded edges and corners so as to prevent point concentration of an electric field, an electrode member adjacent the spacer element at a side opposite the material, a heat resistant resilient member disposed between said spacer member and said electrode to equalize and distribute pressures, said press element extending beyond and overlapping said spacer element so as to cause an electric eld to be directed inwardly towards said spacer element thereby preventing destructive arcing at the edges of the material.

6. Apparatus for dielectrically heating and working heat and pressure sensitive material comprising, in combinaton, an electrically conductive spacer element and a press element disposed on opposite sides of the material in pressing relation therewith, said spacer member having a heat` resistant resilient member between the material and the spacer member, ari electrode member adjacent said spacer element at a side opposite the working material, means for applying high frequency voltage between said press element and said electrode member to dielectrically heat the material, another heat resistant resilient member disposed between said electrode member and said spacer element, said heat resistant resilient members functioning to distribute pressures and stabilize heat variations, said press member extending beyond and overlapping said spacer member so as to cause an electric field to be directed inwardly towards said spaced member, said spacer member spacing the material a predetermined distance from said electrode member, the spacing and directing by said spacer member preventing destructive arcing at the edges of the material.

7. Apparatus for dielectrically heating and embossing heat and pressure sensitive material with one side having a metalized surface comprising, in combination, an embossing die and an electrically conductive portable image die disposed on opposite sides of the material, the metalized surface of the material facing the embossing die, said dies being relatively movable into pressing relation with the material, said embossing die being adapted to function as an electrode, an electrode niember functioning as another electrode supporting said image die, said dies having rounded edges and corners to prevent point concentration of an electric field, and means for applying high frequency voltage between said embossing die and said electrode member, said press element extend- 4ing beyond and overlapping said image die so as to cause an electric iield to be directed inwardly towards said image die, said image die spacing the material a predetremined distance from said electrode member, the spacing and directing by said image die preventing destructive arcing at the edge of the material.

8. Apparatus for dielectrically heating and embossing heat and pressure sensitive material comprising, in combination, a movable embossing die and an electrically conductive portable image die disposed on opposite sides of the material, the material having a peripheral size greater than said image die and less than said embossing die, said embossing die adapted to function as an electrode, a heat resistant resilient member being disposed between the material and the image die, a stationary electrode member functioning as another electrode and supporting said image die, another heat resistant resilient member between said electrode member and said image die, said dies having rounded edges and corners so as to prevent point concentration of an electric field, and means for applying high frequency voltage between said embossing die and said electrode member with the embossing die in pressing ,relation with the material,

Yto function Ias an electrode and an electrically conductive transportable spacer die disposed adjacent said press die, said spacer die being of a predetermined thickness and of a smaller peripheral size than said press die so as to control arcing, said press and spacer dies having rounded boundary edges to prevent point concentration of an electric field and an electrode member supporting said spacer die.

10. Die structure for use in delectrically heated press apparatus comprising, in combination, a press die and an electrically conductive transportable spacer die oppositely disposed with the press die extending beyond and overlapping the spacer die, said spacer die having a heat resistant resilient member disposed along a side opposite the press die and another heat resistant resilient member disposed on the opposite side of the spacer die, and an electrode member next to said other heat resistant resilient member, said spacer die being of a predetermined thickness and of a smaller peripheral size than said press die so as to control arcing.

References Cited in the le of this patent UNITED STATES PATENTS 1,806,846 Fox et al May 26, 1931 1,997,263 Meissner Apr. 9, 1935 2,526,697 Scott Oct. 24, 1950 2,526,699 Gard Oct. 24, 1950 2,536,316 Schwartz et a1 Jan. 2, 1951 2,578,209 Schwartz Dec. 11, 1951 2,595,502 Aicher et al. May 6, 1952 FOREIGN PATENTS 577,719 Great Britain May 27, 1946 621,514 Great Britain Apr. 11, 1949 UNITED STATES PATENT oFFICE CERTIFICATE OF CORRECTION `asstent' Nm 29,920,172 January 5, 1960 Ralph M., S'ballard Itis hereby certified that error appears in the printed specification of the]` above numbered patent requiring correction and that the said Letters Patent should readI as corrected below.

`ioluntn l51V line 4.7 for "object sand" read yobjects( and h; column 3, line 8s "for "My eliminating" read if By eliminating column w line 35,

for "spaced" readyspacer esi; line 58, for "edge" read edges Signed and sealed this Y'7th day oi' June' 1960.

Attest:

Attesting Oflcer KARL AXLTNE ROBERT C. WATSON Commissioner of Patents UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION paient NO @920,172 January 5, 1960 Ralph' M Stellard It: s hereby certified that error appears in the printed specification of the'abov'e numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Gofum L$1 line 4.7,. for "object send" read f'- objects' and ew; eelumn 3, line 8, `lfor "My eliminating" read me By 'eliminating column 4, line 35, `for "spaced" read' yspacer -sf-g linek 58, for "edge" read k edges .Signed yamd sealed this "7th day of une- 1960,

.-fgsEAL Attest:

KAEL AELTNE ROBERT C. WATSON Attesting Ocer Commissioner of Patents 

